This invention relates to motor vehicle fuel economy indicating systems and, more particularly, to a fuel economy indicating circuit for indicating to the operator of a motor vehicle that the vehicle is operating under conditions likely to produce poor fuel economy.
Various fuel economy indicating devices have in the past been proposed for providing the vehicle operator with an indication of the likelihood of poor fuel economy being achieved. Perhaps, the earliest device utilized was a vacuum gauge located within the passenger compartment of a motor vehicle to provide the operator thereof with an indication of engine intake manifold vacuum level. Generally, the greater the manifold intake vacuum, the better the fuel economy. In this connection, manifold vacuum provides an inference of the load on the engine of the motor vehicle.
Vacuum gauges for indicating fuel economy generally have been replaced by warning light indications of manifold vacuum level. Typically, a switch controlled by manifold vacuum energizes a warning indication, such as a red light, when the vacuum level falls below a predetermined threshold, and when the vacuum level is above the threshold, a light indicative of good fuel economy, for example a green light, may be energized to indicate this condition.